1. Field of the Invention
The present invention relates generally to data transmitting techniques and more particularly to techniques for transmitting parallel command and status data with as few data lines as possible.
2. Description of the Prior Art
Conventional techniques for interconnecting a controller, such as a computer, to a controlled device, such as a printer, provide for a command bus typically including a plurality of electrical conductors between the computer and printer and, similarly, a status bus, also including a plurality of electrical conductors between the printer and computer. In a number of installations, this technique functions adequately but, in installations where the computer may be a relatively great distance from the controlled printer the command and status buses connected between the computer and printer must be relatively long, multiconductor cables which are quite expensive.
Also, particular applications require that no electromagnetic radiation, generated by the high speed data processing circuits, be emitted from the computer equipment. To insure that such radiation is not emitted, it is necessary to pass each wire that leaves the computer installation through a relatively elaborate electromagnetic radiation filter. Thus, a large number of expensive filters are required in order to interconnect the controller and printer through the command and status buses.
Thus, there has long been a need in the data processing field for a technique for interconnecting the command and status buses of a controller and controlled device over relatively long distances, and without electromagnetic radiation, which would not require long lengths of expensive cable nor an elaborate array of radiation filters. The present invention satisfies that need.